American Ornithologists' Union's "List of the 2,046 Bird Species (With Scientific and English Names) Known From the A.O.U. Check-list Area" (AOU Check-list, 7th edition, updated with Supplements 42-48), maintained at http://www.aou.org/

Disclaimer:
ITIS taxonomy is based on the latest scientific consensus available,
and is provided as a general reference source for interested parties.
However, it is not a legal authority for statutory or regulatory purposes.
While every effort has been made to provide the most reliable and up-to-date
information available, ultimate legal requirements with respect to species
are contained in provisions of treaties to which the United States is a
party, wildlife statutes, regulations, and any applicable notices that have
been published in the Federal Register. For further information on U.S.
legal requirements with respect to protected taxa, please contact the
U.S. Fish and Wildlife Service.